| Method for measuring gaseous species by derivation -> Monitor Keywords |
|
|
 
Method for measuring gaseous species by derivationRelated Patent Categories: Radiant Energy, Invisible Radiant Energy Responsive Electric Signalling, Infrared Responsive, With Means To Transmission-test Contained Fluent MaterialMethod for measuring gaseous species by derivation description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060202123, Method for measuring gaseous species by derivation. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The present invention relates to a method and to a device for measuring the quantity of chemical species contained in a high-temperature gas and especially the quantity of CO and/or CO.sub.2 contained in a gas output by a metal treatment furnace, and especially an electric arc furnace (EAF) or a basic oxygen furnace (BOF) or converter. [0002] The invention is aimed more particularly at providing a solution for the continuous chemical analysis of the flue gases, collectively called off-gas, from an electric arc furnace, said off-gas being at high temperature (around 1800.degree. C.) and laden with dust (100 to 200 g/Nm.sup.3). [0003] By continuously analyzing the off-gas of a furnace it is possible to obtain information about the treatment process: material and energy balance, state of the chemical reactions inside the furnace, etc. The systems for analyzing the composition of the off-gas, especially that output by an electric arc furnace, must withstand a particularly hostile environment, firstly because of the high temperature of the off-gas (around 1800.degree. C.) and secondly because of the high dust concentration (100 to 200 g/Nm.sup.3), this dust also being very fine (down to 1 micron in size). [0004] A first method, developed by the Applicant and known by the commercial name ALARC AS (and described for example in U.S. Pat. No. 5,344,122) consists in taking samples of off-gas and analyzing these samples: a water-cooled sampling probe is placed in the gap that exists between the outlet of the furnace and the gas exhaust duct of the furnace so as to withdraw a sample and take it into a region where the dilution with ambient air is minimal. The sample thus has a composition representative of the chemical composition inside the furnace. The sample is filtered and then conveyed via a heated line (heated so as to prevent the temperature dropping below the dew point of water, and therefore preventing this water from condensing) to a dryer and then to the various analyzers used: infrared analyzers for measuring the carbon monoxide and carbon dioxide concentrations, thermal conductivity analyzers for measuring the hydrogen concentration, and electrochemical or paramagnetic cells for measuring the oxygen concentration. [0005] However, such a system has a number of drawbacks: [0006] response time: to prevent the filters and dryers from clogging up too rapidly, the withdrawal rate is low. Since the analyzers must be located in areas where the temperature conditions are stable (environmentally controlled box or room), the analyzers are often located relatively far from the sampling point, resulting in a large dead volume. Associated with a low rate, the response time of the analytical system is long, ranging from around 30 seconds to 3 minutes; and [0007] maintenance: with the large quantity of dust in the off-gas, the filters are rapidly saturated therewith. Likewise, inside the sampling probe, the mixture withdrawn, consisting of dust and locally condensed water, rapidly forms a sealed plug. Unclogging cycles are provided so as to unclog this orifice with compressed air or nitrogen, but the long-term operation requires frequent maintenance (to change filters, to clean or replace the sampling probes, etc.) which, depending on the type of installation, is restrictive to a greater or lesser extent. [0008] Another known method consists in using a coherent light beam emitted by a laser source, and especially a diode laser whose wavelength can vary within a certain wavelength range (for example a TDL or tunable diode laser). [0009] The measurement of the composition of a gas by spectroscopy, especially using laser radiation, is based on the property of gas molecules to absorb radiation at characteristic wavelengths (defined by the absorption spectrum specific to each molecule of the gas). [0010] U.S. Pat. No. 5,984,998 (or WO-A-99/26058) and CA-A-2158516 disclose a laser radiation system for measuring the absorption spectrum of the off-gas in the gap in order to measure the CO and O.sub.2 concentrations of this off-gas. However, certain systems use a wavelength range lying in the middle of the wavelength range corresponding to the infrared (also called the "mid-infrared"). This has the drawback of requiring cryogenically cooled lasers--apart from their high cost, these instruments lack flexibility and cannot be easily transported. [0011] WO-A-01/33200 discloses a system for analyzing the off-gas using a TDL operating in the wavelength range corresponding to the infrared near the visible (called the "near-infrared") allowing measurements by laser absorption spectroscopy of the various constituents: CO, CO.sub.2, O.sub.2, H.sub.2O, etc. One of the advantages of this type of instrument and method is that low-power diode lasers are used, which emit radiation in wavelengths close to those intended in general for telecommunication, and conveyed in optical fibers, said fibers, tailored to such wavelengths, being available to bring, without appreciable loss, the radiation output by the diode laser right to the off-gas duct or gap. The radiation then passes through the off-gas duct or gap, is partly absorbed by the molecules that it is desired to analyze, and is received by a receiver. [0012] This particularly effective system does, however, under certain circumstances, prove to be difficult to use when the off-gas to be analyzed has a high dust content: for example, it is very quickly observed that, during operation of an electric arc furnace, the light signal received by the receiver located at the gap becomes, after a few minutes, too low to be interpreted. Thus, application WO-A-01/033200 proposed placing a screen over at least part of the width of the off-gas duct, acting as a deflector and preventing the stream of dust-laden off-gas from attenuating the light radiation too greatly. The drawback of such a system is the insertion of a fitted part that is permanently present in the off-gas duct where the temperature is around 1500.degree. C. WO-A-02/090943 describes a similar solution, which has the same drawbacks. [0013] The problems inherent in a measurement based on a light beam emitted by a diode laser passing through the off-gas duct at the gap of an electric furnace may be summarized thus: [0014] loss of signal: when the concentration of dust particles becomes too high, their scattering (the particles are approximately spherical, with a diameter of the order of the wavelength of the laser) attenuates the transmitted intensity of the laser, and the recovered signal has an amplitude such that the signal/noise ratio is too low for this signal to be exploitable; [0015] species measured: in the near-infrared and at temperatures around 1500.degree. C., not all the lines of the chemical species it is desired to measure are exploitable. This is because, in order to be able to determine a species accurately, without interference from another species, the absorption line that characterizes this species must be sufficiently separate from the characteristic lines of the other chemical species likely to be present in the off-gas. The variation in temperature affects the distribution and the intensity of the absorption peaks: the wavelengths used at room temperature for measuring a given gas can in general no longer be used at other temperatures. For example, for wavelengths in the near-infrared, the absorption lines characteristic of CO.sub.2 can no longer be measured accurately above about 200.degree. C. The CO.sub.2 concentration therefore cannot be measured directly in the gap, where the temperatures reach 1400 to 2000.degree. C. using laser radiation in the near-infrared. In the case of an oxygen concentration measurement for example, this problem is aggravated by the low emission power of commercially available diode lasers in the range of wavelengths in question: with a high dust content, the transmitted power is too low to provide a reliable signal; and [0016] measurement accuracy: two phenomena upset the accuracy of a direct measurement in the gap. Firstly, the presence of dilution air, which is entrained by the hot gas via this opening and which cools said gas, while causing combustion of the carbon monoxide leaving the furnace. Knowing that the concentration measurement given by the diode laser is the absorption averaged over the path taken by the radiation, the composition of the dilution air and its effects have an effect on this calculation. The measurement is therefore less representative of the atmosphere in the furnace. Secondly, the temperature conditions also disturb the accuracy of the measurement: at high temperature, the water absorption lines are omnipresent and greatly confuse the measurement and increase the uncertainty. [0017] According to a first aspect, the invention aims to measure, in particular and preferably, the CO and CO.sub.2 concentrations, and optionally the O.sub.2 and H.sub.2O concentrations, in the off-gas output from a furnace with a response time of less than 10 seconds, usually around 5 seconds, making it possible in particular to control the furnace in real time by overcoming the aforementioned drawbacks. [0018] Another aspect of the invention relates to the blocking of the gas sampling lines due to dust in the off-gas, as explained above. [0019] EP-A-0462898 teaches a method of taking a sample and analyzing it, using a water-cooled sampling probe placed in the gas exhaust duct of the furnace so as to draw off a sample into a region where the dilution with air does not corrupt the measurement. The sample thus has a composition representative of the chemical composition inside the furnace. The sample is filtered and then conveyed via a heated line (heated so as to prevent the temperature falling below the dew point of water) as far as means for extracting this water vapor, and then to the analyzers. These are those commonly used, namely infrared analyzers for carbon oxides, thermal conductivity analyzers for hydrogen, and electrochemical or paramagnetic cells for oxygen. [0020] The problems inherent in a sampling system followed by conventional analyzers are the following: [0021] response time: to prevent the filters and dryers from clogging up too rapidly, the withdrawal rate is low. Since the analyzers must be located in areas where the temperature conditions are stable (environmentally controlled box or room), the analysis bay is often located relatively far from the sampling point, resulting in a large dead volume. With the low rate, the response time of the analytical system is considerable (between 30 seconds and 3 minutes); and [0022] maintenance: with the large quantity of dust in the off-gas, the filters are relatively rapidly saturated therewith. Likewise, inside the sampling probe, the mixture withdrawn, consisting of dust and locally condensed water, rapidly forms a plug that blocks off the gas passage. Unclogging cycles are provided, by blowing compressed air or nitrogen, but the long-term operation requires frequent maintenance (to change filters, to clean or replace the sampling probes, etc.) which, depending on the type of installation, is restrictive to a greater or lesser extent. [0023] The method according to the invention is characterized in that a portion of the gas to be analyzed is taken off, its temperature is lowered down to less than 300.degree. C., preferably down to a temperature of 200.degree. C. or below, so as to obtain a gas with a temperature between 300.degree. C., preferably 200.degree. C., and room temperature, and then at least the quantity of CO and/or CO.sub.2 present in this gas is measured by means of the coherent light signal that is emitted by a diode laser through said gas and recovered upon emerging from said gas. [0024] The coherent light beam may be reflected in a known manner using a mirror and sent back through the gas to be analyzed, or else recovered directly upon emerging from the gas. It is conveyed via an optical fiber and/or converted directly into an electrical signal, in a manner known per se. [0025] According to the invention it is thus possible to measure a single species, whatever the species, but also several species and especially a species chosen from CO and/or CO.sub.2 and/or O.sub.2 and/or H.sub.2O. It is also possible to measure the temperature of the gas in the gap directly using a diode laser by measuring the adsorption of two lines of any one species within the range of wavelengths continually scanned within the wavelength range of the TDL, or else by using a temperature sensor, in a manner known per se, preferably with the aid of a diode laser emitting in the near-infrared, preferably including the 1581 nanometer wavelength. [0026] According to another aspect of the invention, the aim of the latter is to provide an effective system for automatically unclogging the sampling probes for taking dust-laden gas samples, and especially one that is applicable to the system described in the abovementioned patent application. Combined with a pneumatic unclogging device is a moving part that removes, during each unclogging operation, the dust that has built up in the probe. This type of unclogging operation gets round the problem of the accretion of dust and water that attaches to the walls of the probe and that is not removed by blasting with compressed air. The maintenance operations carried out on the probe are therefore greatly reduced and sampling is available throughout the heat. [0027] The essential part of these unclogging means consists of a rod with at least two fins that can be rotated, for example by means of an air cylinder, so as to sweep substantially the entire inner wall of the probe in which these fins move. The rotation is accompanied by a blast of compressed air (either at the same time or afterwards) which expels the dust accretions on the wall. [0028] Preferably, in this unclogging system (in order to draw off the minimum amount of dust while still taking a sample from a region representative of the atmosphere in the furnace), the end of the sampling probe will be beveled and the probe placed so as to draw off, preferably countercurrently, the flow of off-gas. The orifice via which the gas is conveyed is thus protected from being directly splashed, for example with slag, thereby preventing this end from becoming blocked. [0029] More particularly, this other aspect of the invention relates to a system for unclogging a probe of axial symmetry for taking samples from a gas stream containing impurities. [0030] The system according to this aspect of the invention is characterized in that it comprises a part that can move about the axis of symmetry of the probe and can remove the impurities that have built up on the internal wall of said probe by relative rotation of the part and/or of the probe about the axis. [0031] According to a preferred embodiment, this system is characterized in that it includes additional pneumatic unclogging means using compressed air. Continue reading about Method for measuring gaseous species by derivation... Full patent description for Method for measuring gaseous species by derivation Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method for measuring gaseous species by derivation patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Method for measuring gaseous species by derivation or other areas of interest. ### Previous Patent Application: Detecting gas in fluids Next Patent Application: Detector array and cross-talk linearity connection Industry Class: Radiant energy ### FreshPatents.com Support Thank you for viewing the Method for measuring gaseous species by derivation patent info. IP-related news and info Results in 0.14919 seconds Other interesting Feshpatents.com categories: Daimler Chrysler , DirecTV , Exxonmobil Chemical Company , Goodyear , Intel , Kyocera Wireless , 174 |
 * Protect your Inventions * US Patent Office filing 
PATENT INFO |
|
